A collaborative project has been outlined to sort mouse chromosomes for the purpose of generating IRS-PCR (inter-spersed repeat) probes to be used for contig mapping of the mouse chromosome. Interleukin-2 stimulated spleen cells from the strain C57BL/6J are used for sorting different chromosomes. Appropriate Robertsonian strains in a C57BL/6J background can also be used to purify chromosomes that are resolvable in bivariate profiles (10+13, 14+15, and 4+5).